Wind power is considered one of the cleanest, most environmentally friendly energy sources presently available, and wind turbines have gained increased attention in this regard. A modern wind turbine typically includes a tower, generator, gearbox, nacelle, and one or more turbine blades. The turbine blades capture kinetic energy from wind using known foil principles and transmit the kinetic energy through rotational energy to turn a shaft coupling the rotor blades to a gearbox, or if a gearbox is not used, directly to the generator. The generator then converts the mechanical energy to electrical energy that may be deployed to a utility grid.
To ensure that wind power remains a viable energy source, efforts have been made to increase energy outputs by modifying the size and capacity of wind turbines. One such modification has been to increase the length of the turbine blades. However, as is generally known, the deflection of a turbine blade is a function of blade length, along with wind speed, turbine operating states and blade stiffness. Thus, longer turbine blades are subject to increased deflection forces, particularly when a wind turbine is operating in high wind speed conditions. These increased deflection forces not only produce fatigue on the turbine blades and other wind turbine components, but may also increase the risk of the turbine blades striking the tower. A tower strike can significantly damage a turbine blade and the tower and, in some instances, can even bring down the entire wind turbine.
Devices and systems are known for detecting turbine blade deflection using various types of active or mechanical sensors. U.S. Pat. No. 6,619,918 describes the use of fiber optic strain gauges on the turbine blades to measure load on the blades and to deduce tip clearance as a function of the measured load. U.S. Pat. No. 7,059,822 describes a system wherein beams are coupled to the blades and deflection of the blades is determined as a function of the amount of deflection of the beams. U.S. Pat. No. 7,246,991 describes a control system for avoiding a tower strike that uses a signal from a sensor that measures deflection of the turbine blades. Several possible sensor types are described, including strain gauges, accelerometers mounted in the blades, and active radar devices.
The conventional sensors and associated systems are relatively complex and costly, and calibrating such sensors can be quite complex and time consuming. Moreover, the sensors are generally limited to detecting the presence of the blade at a single circumferential location on the tower. However, the nacelle can assume virtually any rotational position relative to the tower, which may result in the blades passing the tower on the opposite side of the sensor (i.e., receiver or transmitter component) mounted on the tower.
Accordingly, there is a need for a blade deflection sensor system that is mechanically simple, robust, and provides reliable detection of the blade around the entire circumference of the tower.